The present invention relates to a novel fluorine-containing polymer compound, a positive-type resist composition using the same, and a pattern forming process by the same.
It is not possible to form fine patterns of semiconductor integrated circuits, if exfoliation or falling down of resist pattern occurs. Therefore, it is necessary to have adhesion between resist film and substrate.
As a method for improving adhesion between resist film and substrate, there is a proposal to introduce a hydrophilic lactone ring (e.g., γ-butyrolactone of 2-oxo form or γ-butyrolactone of 3-oxo form) into a polymer compound constituting the resist. Furthermore, there is a proposal to introduce a polymerization unit containing a hydrophilic polar group, such as carboxyl group (Japanese Patent Application Publication 2006-065071) or hydroxy group, into a polymer, as a means for improving adhesion of resist film.
A polymer having a hexafluoroisopropanol group, which contains a hydroxy group, can provide a resist composition superior in transparency and development property and a relatively good resist pattern. There is, however, a problem in which it is not possible to form a fine resist pattern, since a pattern falling down occurs by penetration of a developing solution into an interface between resist film and substrate. A method of using a carboxyl group can improve alkali solubility and adhesion to substrate. With this, however, the polymer may become too strong in water absorption by the introduction of carboxyl group. Therefore, swelling tends to occur in alkali development after exposure, and it becomes difficult to obtain a stable pattern in a finer lithography. Furthermore, in the case of increasing the number of carboxyl groups in a carboxyl-containing polymer to strengthen its action, alkali solubility increases. With this, however, swelling tends to occur in alkali development after exposure, since the polymer becomes too strong in water absorption by the introduction of carboxyl groups. Furthermore, a pattern falling down tends to occur by penetration of a developing solution into an interface between resist film and substrate. Furthermore, there is a proposal of a polar polymer having both of a carboxyl-containing unit and a lactone ring-containing unit (Japanese Patent Application Publication 2005-075859).
Thus, there has been not yet provided a resist polymer that can suppress dissolution of pattern itself, swelling of pattern, etc., that can provide a superior adhesion between resist film and substrate, and that can suppress the occurrence of pattern exfoliation, pattern falling down, etc.
As carboxylic compounds having a fluorine atom at α-position, 2-fluorophenylacetic acid and its ester (see Japanese Patent Application Publication 1-242551) and ethyl 2,2-difluoro-3-hydroxy-3-phenylpropionate (see Tetrahedron Letters, Vol. 25, No. 22, pp 2301-2302, 1984) are known.